The present invention describes an improvement to and extension of the channel signal processing method described in copending application U.S. Ser. No. 07/270,895, filed Nov. 14, 1988 now U.S. Pat. No. 4,945,538.
While the method described in this cited earlier filed application operates satisfactorily, the data rate of the (1,7) coded partial response channel employed therein is limited by the speed of the electronic circuits in a given VLSI technology; more particularly in the time it takes to perform an 8-bit add operation and store it in a register. Also, it describes a five-sample look-ahead algorithm for processing channel sample values which works well when all error modes are caused by similar noise circumstances. However, in specific applications, such as magnetic and optical recording, when the readback pulse is distorted towards being too wide, the available distance is reduced for one particular pair of sequences of sample values. The reliability performance of the decoder, in that case, is predominantly determined by the lower margin of error associated with these sequences.
There is a need for an improved method and means for processing sample values in a coded signal processing channel that employs a look-ahead algorithm that is restructured to increase the data rate by allowing n cycles per operation and decoding n bits at a time.
There is also a need, in such a method, for an algorithm which, by providing additional information from a six- (rather than five) sample look-ahead, achieves higher reliability in signal detection and increased tolerance to distortion of the readback pulse.